How does Teradata determine primary index?
Choose columns for the primary index that distribute table rows evenly across the AMPs. The more singular the values for a column, the more optimal their distribution. Choose as few columns as possible for the primary index to optimize its generality.
How many primary indexes are there?
Primary index is defined while creating a table. There are 2 types of Primary Indexes.
Which field will be selected by Teradata as the primary index?
If you don’t define an index, Teradata will implicit take the first row as Primary Index. Beside this you can either choose a or many columns as Primary Index or define the table by NO PRIMARY INDEX. Primary Index will define the Distribution Key of the data across the AMPS.
Where is primary key in Teradata?
If you explicitly define a primary key in the table definition, teradata will maintain it with indextype = ‘K’ in the DBC. Indices view. Otherwise you are stuck to looking for unique indexes via uniquenessflag = ‘y’ in dbc. indices ( club on the index number for composite indexes) …
What is secondary index in Teradata?
A Secondary Index (SI) is an alternate data access path. It allows accessing the data without having to do a full-table scan. The secondary index can be created explicitly using the CREATE TABLE and CREATE INDEX statements. Teradata Database can implicitly create unique secondary indexes.
What is difference between primary key and primary index?
The primary index is created automatically when the table is created in the database. Primary key is mandatory.it avoid the duplicate of data. for ex (student rollno, material no, employee id)it should be a unique. when you create the foreign key in the particular table before it should be one primary key.
Can primary key be null in Teradata?
15.00 – 5516 PRIMARY KEY or UNIQUE column(s) must be NOT NULL. – Teradata Database.
What is the difference between primary key and primary index?
What is primary & secondary indexing in Teradata?
Secondary indexes are an alternate path to access the data. There are some differences between the primary index and the secondary index. Secondary index is not involved in data distribution. Secondary index values are stored in sub tables.
What is USI and nusi in Teradata?
USI is hash ordered; the same hash function used in the primary index is used. NUSI, on the other hand, is value ordered, so each AMP maintains its own sorted list of values. Helpful (0)